Active transport: An in vitro hemi-atrium preparation will be developed that used the thin myocardial membrane of skates, toads and turtles to characterize amino acid transport, particularly of the beta sulfonate taurine. Appropriate competitive inhibitors will be used to analyze kinetics in flask and "Ussing chambers", and to seek possible relationships of taurine uptake to beta-adrenergic stimulation and calcium fluxes. Isolated renal tubules of the flounder will be used to determine whether disulfide reagents such as sodium tetrathionate and 6,6'-dithiodinicotinic acid, as well as phlorizin, exert a biphasic effect on organic acid transport, i.e., transient stimulation followed by inhibition. Transport at both the luminal and contraluminal sites will be characterized. Pharmacogenetics: The effect of a genetically determined circulating atropinesterase on dose-response relationships of atropine to an apneic reflex in rabbits will be studied. Action of the drug on heart rate, peripheral resistance and arterial pressure will be measured in rabbits having high, intermediate and no enzyme activity.